Priority is claimed to Patent Application Numbers 2001-23227 filed in Rep. of Korea on Apr. 28, 2001 and 2002-19298 filed on Apr. 9, 2002, herein incorporated by reference.
1. Field of the Invention
The present invention relates to an evaporator having a structure for circulating working fluids by capillary action, and more particularly, to a flat evaporator having a capillarity generator that surrounds a vaporization cavity region.
2. Description of the Related Art
As electronic technologies have advanced, electronic devices tend to be designed as modules and have smaller dimensions and higher output capabilities. Heat generated per unit area of electronic devices continues to increase accordingly. Thus, it is of great concern to properly control heat generated in electronic devices in designing and operating the electronic devices. There are several well-known techniques for controlling temperature in electronic devices including: thermal conduction, natural convection/radiation or forced convection of air, cooling by a liquid, immersion, distribution of heat through heat pipes.
A capillary pumped loop (CPL), which has recently been developed, is a system in which surface tension at boundaries where phase change of a coolant occurs is used as a driving source for transporting the coolant. A cooling system employing this CPL includes an evaporator for transferring heat from a heat source using a gas coolant and a condenser for condensing the gas coolant output from the evaporator into a liquid.
CPL evaporators must be constructed such that heat generated from a heat source effectively promotes phase change of a coolant and that boundaries where phase change of the coolant occurs are evenly distributed around a heat source since surface tension at the boundaries is a driving source for transporting the coolant.
A cooling system devised by Stenger of NASA Lewis Center is constructed by a loop in which a coolant flows through a pipe. The loop consists of an evaporator portion having a porous body that generates capillary action on a path along which the coolant flows at one end of the pipe. The loop is configured to condense the coolant by giving up heat at the other end of the pipe. Since it is difficult to make the pipe loop smaller, this structure is not suitable for electronic instruments or equipment of smaller dimensions.
U.S. Pat. No. 5,725,049 by Swanson et al., describes a flat heat exchanger employing a CPL. The heat exchanger proposed in the above patent includes an evaporator, a condenser, a liquid tube, and a vapor tube. The evaporator has top and bottom bodies, and a porous body between the top and bottom bodies thereof. Grooves connected to the liquid tube are formed in a top portion of the porous structure, and grooves connected to the vapor tube are formed in a bottom portion thereof. The heat exchanger is configured so that a liquid coolant supplied from a central portion of the top grooves of the porous structure disperses into adjacent grooves to vaporize the liquid coolant through the porous structure thereby outputting vapor to the vapor tube through the bottom grooves thereof. However, because of its structure, the heat exchanger cannot be used as a cooling device for a heat source having a small surface area but high heat generation or a small thin cooling device.
To solve the above problems, it is an object of the present invention to provide a flat evaporator having small and thin dimensions.
It is another object of the present invention to provide a flat evaporator having small dimensions and high cooling efficiency.
Accordingly, to achieve the above objects, the present invention provides a flat evaporator including: a substrate having on the top surface a vaporization cavity region with a central chamber in which main evaporation of a liquid coolant occurs, a capillary region surrounding the central chamber, and a manifold region surrounding the capillary region; a top plate disposed on the substrate; a capillarity generator which is formed in the capillary region and flows the coolant from the manifold region into the vaporization cavity region by capillary action; an exhaust unit which includes a gas collector and exhausts a gas coolant generated in the vaporization cavity region; and a supplying unit including a coolant supply portion to supply the liquid coolant from the outside to the manifold region.
The present invention also provides a flat evaporator comprising: a substrate having on the top surface a vaporization cavity region with a central chamber in which main evaporation of a liquid coolant occurs, a capillary region surrounding the central chamber, and a manifold region surrounding the capillary region; a top plate disposed on the substrate; a capillarity generator which is formed in the capillary region and flows the liquid coolant from the manifold region into the vaporization cavity region by capillary action; an exhaust unit which includes a gas collector and exhausts a gas coolant generated in the vaporization cavity region; a plurality of adiabatic regions which divide a liquid coolant path in the manifold region into a plurality of flow paths and prevent heat from being transferred to the liquid coolant flowing along the plurality of flow paths; and a supplying unit including a coolant supply portion to supply the liquid coolant from the outside to the manifold region.
In one alternative embodiment of the present invention, the capillarity generator may be implemented with a porous body having a plurality of cavities and capable of generating capillary action. In another alternative embodiment, the capillarity generator may be implemented with a wick structure for providing a coolant flow gap between the vaporization cavity region and the manifold region.
In a flat evaporator according to the present invention, it is preferable that the gas collector is formed of a size large enough to cover only the vaporization cavity region or both of the vaporization cavity region and the capillary region. It is preferable that a coolant inlet passage extends from one side of the substrate or the top plate to the manifold region, and a coolant output passage extends from one side of the top plate to the gas collector.
In a flat evaporator according to the present invention, it is preferable that a groove is formed at the bottom of the top plate corresponding to only the manifold region or both of the manifold region and the capillary region, thereby increasing the entire volume of the manifold region. It is preferable that a first auxiliary capillary generator is formed at the bottom of the central chamber, and the first auxiliary capillary generator is formed of a porous body and/or a wick structure. More preferably, a second auxiliary capillary generator is formed at the bottom of the manifold region, and the second auxiliary capillary generator is formed of a porous body and/or a wick structure.
To evenly supply a coolant into the vaporization cavity region to induce uniform evaporation over the vaporization cavity region, it is preferable that the capillary region is formed to asymmetrically surround the vaporization cavity region, and the width of the capillary region is larger towards the coolant supply portion. Preferably, the width of the manifold region surrounding the capillary region is larger farther away from the coolant supply portion. In an alternative embodiment, two coolant supply portions can be symmetrically disposed at opposite sides of the center chamber so that the liquid coolant is supplied through the two coolant supply portions into the manifold region.